Adherence of the oral pathogen Porphyromonas gingivalis to oral epithelial cells is an important event in the pathogenesis of periodontal disease, as indicated by the observation that mutants of P. gingivalis that do not express fimbriae are attenuated in virulence. Patients with periodontal disease have high titers of anti-fimbrial antibodies, and rats immunized systemically with purified fimbriae are protected against the damaging effects of P. gingivalis infection. These data strongly suggest that immunization with fimbriae may provide protective immunity against P. gingivalis-associated periodontal disease. The GOAL of this project is to investigate the potential of using a type II heat-labile enterotoxin (LT- IIa) of enterotoxigenic Escherichia coli as a co-immunogen or carrier of fimbrial antigen in an oral anti-P. gingivalis vaccine. LT-IIa shares similar subunit structure and function with cholera toxin (CT) expressed by Vibrio cholerae. Immunomodulating activity has been demonstrated for CT, in that CT stimulates an enhanced immune response to an antigen when the antigen and the enterotoxin are simultaneously administered as co- immunogens. Adjuvant activity has been correlated with binding activity of CT for ganglioside GMI. Because LT-Ila binds to a wider range of gangliosides than CT, LT-IIa is expected to have a greater adjuvant potential than CT. The SPECIFIC AIMS of this proposal are twofold. 1) We will define the adjuvant activity of LT-IIa in a multicomponent oral anti- fimbrial vaccine. Rats will be immunized subcutaneously (SC) and orally (PO) with purified fimbriae in the absence and presence of LT-IIa, and the ability of LT-Ila to evoke an enhanced immune response to fimbriae will be measured. 2) We will produce fimbrial-based LT-IIa fusion proteins for use as oral vaccines. Chimeric LT-Ila genes will be engineered that encode fimbrial determinants. Hybrid proteins produced by the chimeric genes will maintain the ganglioside-binding activity of the parental LT-Ila enterotoxin, but will express fimbrial determinants as part of a fusion protein. Fusion protein will be purified and tested in rats for ability to evoke an anti-fimbrial immune response. The data obtained herein will be used to develop fimbrial-based vaccines against P. gingivalis disease. In addition, the LT-Ila enterotoxin fusion system will be investigated as a model for vaccine development for other oral pathogens.